1. Field of the Invention
The present invention relates to a silencer and a motorcycle provided with the silencer.
2. Description of Related Art
Some motorcycles comprise an exhaust emission control device, in which a catalyst is mounted in an exhaust silencer and exhaust gases from an engine are purified by contacting the catalyst when passing through the exhaust silencer. JP-A-8-246861, for example, proposes a construction for mounting a catalyst in an exhaust silencer.
JP-A-8-246861 discloses a catalyst mount construction in which an exhaust silencer (silencer) is double-tube structured to include an inner cylinder and an outer cylinder. A catalyst fixed member is provided on an inner peripheral surface of the inner cylinder, a catalyst fixed flange is provided on an outer peripheral surface of a catalyst, and the catalyst is mounted in the exhaust silencer by fixing the catalyst fixed flange to the catalyst fixed member by means of a bolt.
Since the catalyst is fixed to the inner peripheral surface of the inner cylinder in the construction disclosed in JP-A-8-246861, however, the inner cylinder is preferably a straight tube (in the form of a straight cylinder) in order to firmly fix the catalyst, and a shape of the outer cylinder is also determined to some degree according to a shape of the inner cylinder when the inner cylinder is made a straight tube, so that the whole silencer is considerably restricted in freedom of design.
Many large-sized motorcycles, which have a low-speed type V-type engine, have two silencers. If the number of silencers is reduced to one (in view of weight, for example), a decrease in exhaust efficiency results. To increase exhaust efficiency, the silencer diameter may be increased. Thus, in a large-sized motorcycle having a low-speed type engine and a single silencer, the silencer must be large in diameter, which further aggravates restrictions on the layout of the silencer.